Fig. REF  illustrates the distribution of readings in Book-Crossing dataset. Figure REF  indicates that reading counts of books follow a long-tail distribution as expected.
That means a small proportion of books are read by many users, whereas a significant proportion (i.e., the long-tail) is read by only a small number of readers. Additionally, we illustrate in Fig REF  the ratio of popular books to all books read by users. Same as [1]}, we sort books based on the number of readers and consider them as popular if they are within the top-20% of the sorted list. By this definition, we observe that around \(5,256\)  out of \(6,358\)  users (i.e., around \(83\%\)  of users) have read at least 20% of unpopular books in their profile.
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